And the reservoirs of Roosevelt Lake and the Salt and Verde rivers are dwindling.

If the Colorado River is declared in a shortage, Arizona could face its first water supply cut.

The good news, as Kathleen Ferris of the Arizona Municipal Water Users Association points out, is that demand in major cities has actually dropped amid conservation efforts. Per capita water usage has leveled or dropped in many Valley cities over the past five years, according to data from the Arizona Department of Water Resources.

Still, households in some areas use far more water than the average Arizona resident, at 100 gallons per day. Between that 10-minute shower, which could guzzle 20 to 40 gallons, and that gorgeous lawn you fight to maintain, it's easy to rack up the numbers.

A series of interactive maps will document how we use one of Arizona's most precious resources. Beginning with water usage by ZIP codes within the Phoenix Water Services Department coverage area, the maps will build to include other municipalities as well as other information about our water supply.

Metro Phoenix: Which households use the most water?

Paradise Valley residents among highest users

The Republic compiled water usage data from the city of Phoenix to determine the areas that use the most. Click on the ZIP codes to compare how much water the average household uses in a month — and how many 15,000 gallon swimming pools that could fill — as well as demographic information about residents in that area.

To see the map legend, click on the double arrow at the top left corner of the map.

If you live in the 85253 ZIP code, you might be able to fill more than three swimming pools. The Paradise Valley-area ZIP code tops the charts for Phoenix water customers for using the most water per household by consuming about 49,118 gallons a month.

Families typically use up to 70 percent of their water outside, which could help explain the high-use in that ZIP code. Most of Paradise Valley is zoned for 1 acre lots for each house.

Conversely, single-family homes in the Tolleson-area 85353 ZIP code use the least amount of water in the department's coverage area — only enough to fill about half of a swimming pool.

Some of the ZIP codes with the highest median incomes — 85253, 85028, 85254, 85045, 85048 and 85310 — are among the top quarter of water users in the department.

"Wealthier people are less impacted by their water bills, and so they may be less inclined because their water rates go up to use less," Ferris said.

And some of the ZIP codes with the lowest median incomes, such as 85006, 85017, 85034 and 85040, are among the bottom quarter of water users. But the data show many other low- and moderate-income ZIP codes scattered among the department's higher-water-use customers, and other higher-income ZIP codes among the most conservative users.

The Cave Creek-area ZIP code 85087 has the third-lowest poverty rate in the coverage area and ranks in the bottom quarter for water usage. The average family there consumes far less than those in 85003, which has a 34.8 percent poverty rate and is the eighth-highest user. That ZIP code follows Central to Seventh avenues from Thomas Road down to the Salt River.

Ferris said that although the wealthier areas may use more to care for their lawns and pools, they generally use less water indoors than lower-income areas because they tend to install more efficient appliances.

Ferris said a variety of factors affect per capita use and there is no catch-all method for conservation. She advises people to call their water provider directly and ask what they can do to conserve.

Sources: City of Phoenix, Arizona Republic research, Census Bureau

On the beat: Caitlin McGlade

Data reporter digs deep

Caitlin McGlade(Photo: The Republic)

Caitlin McGlade is a data reporter in the News Watchdog Center. She digs through public records, analyzes massive data sets, builds charts and maps, and talks to experts to get to the bottom of the complicated stories you want to learn about.